Fertility program crucial to no-till success

When farmers learn how it’s done, most find little, if any, yield penalty from switching to no-till production practices. And learning how to fertilize no-till crops is a crucial lesson.

“And they get other advantages,” says Lloyd Murdock, University of Kentucky Extension soils specialist.”

Murdock discussed advantages and challenges for no-till production recently at the No-till Oklahoma Conference in Oklahoma City.

“Two-thirds of Kentucky wheat is planted no-till,” Murdock said. “Farmers were reluctant to switch, but found that they save time and labor. And no-till yields are comparable to conventional tillage after they learn how. But it takes a special thought process and time to adjust to no-till.”

Murdock said it took Kentucky growers several years to bring no-till corn yields up to conventional production levels but after about six years no-till production began to compete with conventional in state yield contests. “Consequently, we see no reason to do any tillage,” he said. “Plus, we get other advantages such as reduced runoff.” He said soil loss with no-till is significantly lower than with conventional tillage, 0.16 tons per acre versus 8 tons per acre annually.

“Eight tons is not a lot, about the width of a dime, but it accumulates over the years. The only way to stop the soil loss is with no-till production.”

Murdock said one of the learning curves farmers must master is fertilization. It’s different with no-till. “In no-till production we put fertilizer on top of the soils. Phosphorus and potassium move very little so we build fertility near the soil surface.”

He said no-till farmers can sample much shallower than if they were using conventional tillage techniques. “Four inches is adequate,” he said. “Fertility levels will be lower the deeper you go. With conservation tillage sampling below 6 inches is unnecessary.”

He said phosphorus moves the least, but may move some in sandy soils. “It does not move in clay or heavy soils. Also, leaving residue on the soil surface changes rooting patterns for crop plants. We get a lot of rooting just below the residue layer. Roots pick up the nutrients that don’t move.”

He said phosphorus may move over time, stimulated by biological activity. But even if we plow, we still concentrate nutrients near the soil surface.”

Murdock says potassium stays near the surface, too, even though it moves more than phosphorus.

Murdock said no-till farmers have to pay attention to pH levels. “For one thing, weed control may not be as good. Atrazine, for instance, does not work as well with low pH soils.”

He said the primary cause of low pH is nitrogen fertilization, especially from anything with a lot of ammonia. “Nitrification acidifies the soil,” Murdock said.

It takes 3 pounds of lime for every 1 pound of nitrogen to neutralize soils, he said. “With 250 pounds of nitrogen, we need 750 pounds of lime.”

He said surface applied nitrogen will acidify the top 2 to 3 inches of soil. Altering a 4.6 pH to 6.4 at zero to 2 inches with lime could take five years. “Without lime, a 5.7 pH could drop to 4.6.”

Murdock said no-till farmers also must be alert to potential nitrogen losses in high residue. He said losses occur from immobilization, volatilization, and denitrification. Also, with increased organic matter content, farmers may need a little less nitrogen.

“But there are limits to how much organic matter will accumulate. It depends on the climate. Hot, humid conditions result in less organic matter accumulation than occurs in cooler climates. We have to balance organic matter to limit immobilization.”

“Injection is the best application method,” he said. “Dribbling it on is next.” He said broadcast efficiency depends on the nitrogen source.

“There are a lot of ways to lose nitrogen,” said Brian Arnall who works in Oklahoma State University cropping systems Extension, teaching and research capacities. He said some nitrogen in soil organic matter is not mineralized, “about 4 percent every year. With 2,000 pounds of nitrogen tied up in the soil organic matter, about 80 pounds would be mineralized each year,” Arnall said. That also depends on climate. “Cold, dry soils decrease mineralization; warm moist soils mean nitrogen mineralizes more.”

He said in the first three to five years in no-till production, crops may need more nitrogen. “But that depends. Most of the time it does, but if conditions are perfect for mineralization, it might not. Our best recommendation is that no-till takes a little more nitrogen, early on. Using legume cover crops may help, too.”

He said after five years conventional wisdom indicates no-till “always takes more nitrogen.” That depends, too. “Some years, it may take less. With more organic matter, mineralization increases in some years. Some years nitrogen is immobilized and following high yields, we need more nitrogen.”

He agrees with Murdock that application technique can affect nitrogen loss. “If farmers are surface applying nitrogen, they might need to change. They can lose a lot of urea. “Broadcasting UAN in the fall, however, can help break down residue. Also, no-till will cause layering of nitrogen, phosphorus and potassium.

“Increasing organic matter in the soil is good,” he said.

Arnall said surface application of nitrogen increase potential for loss. “Soil test. And be sure to alert the lab that you are using no-till. Also be aware that a high rate of nitrogen without lime will drop pH quickly.’

He said the best practice is to put nitrogen under the residue to reduce immobilization. “Yields are better with dribble application or injection versus broadcast.” He agrees with Murdock that injection is the best application method.

He recommended that no-till farmers use nitrogen rich strips to judge demand. “Also, rotation with a legume will account for some nitrogen.”

He said for high pH, “about the only solution is to apply sulfur.”

Murdock said no-till production’s penchant for accumulating phosphorus and potassium reduces the need to use a starter fertilizer.